Resin transfer molding, also commonly referred to as RTM, is a process that applies resin to a reinforcement, typically a woven or non-woven reinforcement. When molding, the reinforcement is usually placed on the lower mold, the mold halves clamped together, and resin pumped into the molds under pressure. A compressible seal is built into the mold around the part periphery, with provisions for allowing air to escape while containing the resin.
Resin transfer molding apparatuses typically use a small metering pump that includes a resin cylinder for one-part systems, and separate resin and catalyst cylinders for two-part resin systems. A hand-held static mixer is placed adjacent to or is temporarily fastened to an injection port on the mold. The metering cylinders are cycled until a predetermined volume of resin has been delivered into the mold. The static mixer then is withdrawn and flushed out. Simpler VARTM and RTM systems MAY use pre-mixed resins which have a suitably long working time after mixing
Generally, vacuum assisted resin transfer molding (VARTM) processes include layers of a material of an unimpregnated fiber and/or fabric on top of a mold. A vacuum bag is placed around the lay-up and sealed to the mold. A peel ply may be placed on top of the lay-up and between the layers and mold surface to insure that the vacuum bag can be removed from the completed part and that the part can be removed from the mold. Resin is introduced into the vacuum bag while a vacuum is drawn from beneath the lay-up to cause the resin to flow through the lay-up. Thereafter, the resin flow is terminated and the resin in the assembly is cured, which in some circumstances may require heating the resin to curing temperature. To insure even distribution of resin into the lay-up, a resin distribution medium is placed on top of the lay-up, which is designed to cause the resin to evenly distribute there across eliminating resin-starved areas. It is difficult to ensure complete and even infusion of resin in VARTM systems, however. Also, resin tends to be left in the supply channels and pulled into the vacuum source, which requires additional clean-up that increases costs and can create additional emission of fumes.
There are a variety of resin transfer molding, VARTM, and resin infusion apparatuses. Practitioners have generally not distinguished the type of pump technology that they have used. Frequently, the RTM and VARTM patents have explored alternate ways of distributing resin within the chamber or of creating the forms, but merely refer to “means for providing vacuum” on the chamber.
In traditional resin application systems, excess resin is collected from an application chamber and either disposed of or manually transferred to the supply chamber for the substance. In the VARTM process, it is typical for a trap to be attached to the application chamber. A vacuum system is then used to draw resin into the trap. The trap is intended to prevent substance from being drawn into the vacuum system as it evacuates the application chamber. When it is necessary to move the resin from the trap or other collection vessel to the supply chamber, feed and vacuum tubes are typically closed off by use of valves or clamps. Often, the resin is then collected in a vessel and physically transported to the supply chamber.
In cases where the substance, such as resin, is physically transported in a vessel, the operator must pay ongoing attention to the changing level of the substance in the vessel to avoid an overflow and waste of the substance. An additional disadvantage to the physical handling of a substance in an open vessel is that the substance is exposed to atmospheric air and moisture or dryness that can degrade the substance.